1. Field of the Invention
The present invention relates to a method and an apparatus for cost calculation in motion estimation, and more particularly, to a method for cost calculation in decimal motion estimation and an apparatus thereof.
2. Description of the Related Art
Motion estimation is a significant process in the video compression technique. Its major function is to calculate and compare the costs of motion vectors within a specific range. There are two major methods for decimal motion estimation in the prior art.
The first method is as shown in FIG. 1. In such method, an interpolation is performed on the reference frame data 101 for obtaining the decimal position data (it is indicated in the diagram by “x”), and a cost is obtained by calculating and comparing the interpolated data with the current block 111. Here, the current block is the block in the current frame. As shown in FIG. 1, the block size is 4×4, and the motion vector is headed towards the bottom-right as (0.5, 0.5). The disadvantages of such method are the interpolation is required and the computing amount is proportional to the number of the decimal motion vectors required to test. If it is desired to further support motion estimation for variable-size block, the interpolation may be required for every variation of block sizes and motion vectors, which significantly increases the computing complexity.
The second method is a method disclosed by U.S. Pat. Nos. 5,623,313 and 5,694,179. The second method uses a cost obtained from an integer point motion vector to estimate a cost of the neighboring decimal motion vector. Such method significantly reduces the computing amount required by the interpolation. However, its major disadvantage is the poor accuracy of the estimated cost, which significantly degrades the compression quality.
As described above, the conventional method cannot provide the low computing amount and the high accuracy cost at the same time. Accordingly, it is one of the objects of the present invention to resolve this problem.